I'm wrestling with a note my editor left in my ms. I do NOT see the following as a parenthetical expression, and I think the punctuation is correct as is.

His body was wiry and strong, and the dark eyes that met Lia's were bright with interest and--could it be pity?

The editor wanted me to replace the m-dash with a comma. She said it's a parenthetical expression and thus should have two dashes or two commas. I think she's plain wrong. Am I delusional?